We created space for a pond on a hillside aprx 18 feet x 12 and aprx 5 feet deep. Because there is hardly any top soil and it is very rocky (marl too), it could not retain the water. So we dumped aprx 18 inches of clay. But water still soaks through, how do we make it waterproof? We used some pigs for a while and they did a great job at digging out all the vegetation but they also started to dig out the stones and removed the clay from the sides…. what’s the next step?
Plant the local wetland plants around the water edge and on the banks of the pond. It is my feeling / intuition that plants that live in or near water will be evolved to retain water in their surrounding landscape.
As mentioned above, ducks (with their flat feet) will help form the bottom of the pond.
Reduce evaporation of surface and surrounding soils with shade plantings.